Design And Performance Of Porous Carbon-based Supercapacitors

With the continuous development of modern social science and technology,a variety of electronic equipment are increasingly developed,which stimulates the improvement of high-efficiency energy storage devices and market demand.In recent years,supercapacitors have been widely studied by scientists based on their excellent power density,good cycle stability and safety.At present,commercial supercapacitors are mainly based on carbon-based symmetrical supercapacitors,the serious self-discharge behavior,high cost,and low energy density limit their further applications.Therefore,this thesis has developed a cheap and readily available biomass carbon-based high-performance electrode material and assembled a symmetrical/asymmetrical supercapacitor to increase its energy density;and has development of the new metal-carbon-based electrode material with a Faraday capacitor to assemble asymmetric supercapacitors to further improves their performance;and the self-discharge behavior of carbon-based symmetrical supercapacitors is reduced by preparing a new type of diaphragm.The main research contents and results are as follows:1.Using the cheap and readily available biological waste tinynut shell（TS）as the carbon source,and using KOH as activating agent and pore making agent,the porous carbon material（TSPC-4）based on tinynut shell was successfully prepared by a simple one-step activation and carbonation process.This porous carbon has good electrochemical performance as an electrode material for supercapacitors,and its specific capacitance can reach 280 F g^-1,and the energy density of the assembled symmetric supercapacitor can reach 21.3 Wh kg^-1,which is much higher than commercial supercapacitors(≈10 Wh kg^-1)and most literature data.2.Kelp-based porous nanosheets（AKPC）was prepared by using a kelp as carbon source and a unique method of direct activation and carbonization after swell（NaCl）,which specific capacitance can reach 180 F g^-11 under three-electrode conditions at a current density of 0.5 A g^-1.A novel ball-like MoP₂@Ni₂P nanosheet electrode material was prepared by a simple hydrothermal synthesis reaction followed by low-temperature phosphating process,which the specific capacitance is as high as 133.6 mAh g^-11 at a current density of 0.5 A g^-11 under three-electrode conditions.The potential window of the new asymmetric supercapacitor MoP₂@Ni₂P//AKPC assembled with MoP₂@Ni₂P as the positive electrode and AKPC as the negative electrode can be extended to 1.65 V,and the energy density can reach 31.5 Wh kg^-11 when the power density is 174.4 W kg^-1,the specific capacitance can still retain the initial 81%after 1500 times of continuous charging and discharging.3.A new type of nitrogen-doped iron carbide（N-Fe₃C）porous sheet material was prepared by co-precipitation method and high-temperature calcination method.In the three-electrode condition,it has a higher specific capacitance of 165 mAh g^-11 at 0.5 A g^-1.A one-step hydrothermal synthesis method was used to prepare a cobalt,nickel,and molybdenum ternary metal oxide composite（CNMO）with flower-like nanosheet structure,under the three-electrode condition,the specific capacitance is as high as120.7 mAh g^-11 when the current density is 0.5 A g^-1.An asymmetric supercapacitor assembled with CNMO as the positive electrode and N-Fe₃C as the negative electrode（CNMO//N-Fe₃C）has a wide operating voltage window（0-1.6 V）,an ultra-long cycle performance（After a charge and discharge cycle of 10,000 cycles,its specific capacitance still retains the initial 92.3%）,which greatly improved the energy density of supercapacitors(40 Wh kg^-1).4.A symmetrical supercapacitor was assembled using activated carbon as electrode and a low cost,non-toxic and degradable polyacrylonitrile@sodium dodecylbenzene sulfonate（PAN@SDBS）nanofiber membrane as separator which perpared by using coaxial electrospinning technology.The microstructure of different nanofiber membranes was further analyzed by adjusting the concentration of SDBS,and then used as the separator of commercial activated carbon-based supercapacitors to study its self-discharge behavior.Experiment have shown that the separator can well suppress the self-discharge behavior of supercapacitors via restraining the ion diffusion driven by concentration gradient without sacrificing electrochemical performance.